The present invention relates to a gas component detection apparatus of the type described in the applicant's earlier U.S. application, Ser. No. 662,956, and more particularly to a gas component detection apparatus for detecting the variation in concentrations of gaseous components such as oxygen (O.sub.2), carbon monoxide (CO) and hydrocarbon (HC) of exhaust gases from combustion devices such as an internal combustion engine.
Gas component detection apparatuses have been widely used in many industrial fields. Lately, as a countermeasure to cope with the problem of exhaust gases from an internal combustion engine, gas component detection apparatuses have been employed for determining the air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine.
In the case where a catalyst is utilized for purifying exhaust gases from an internal combustion engine, the catalyst cannot exhibit maximum properties unless the air-fuel ratio of an air-fuel mixture is maintained constantly at a proper value. However, in an ordinary internal combustion engine equipped with a conventional carburetor or a fuel injection apparatus, the air-fuel ratio is actually inevitably subjected to a large variation even when the ratio of injected fuel to intake air is set to be constant. Consequently, in order to maintain constantly a proper air-fuel ratio, it is necessary to detect with the use of gas detection apparatuses air-fuel ratio prior to the burning of the air-fuel mixture and feed back signal corresponding to the detected value to the carburetor or the injection apparatus, thereby controlling the air-fuel ratio of the air-fuel mixture supplied to the engine.
Gas component detection apparatuses are constructed to determine the air-fuel ratio based on the fact that variation in concentrations of gaseous components of the exhaust gases is closely related to variation of the air-fuel ratio of the air-fuel mixture. In this connection, consideration has to be given to the fact that the temperature of the exhaust gases, as well as the concentrations of the gaseous components thereof, will vary abruptly and remarkably. It is thus desirable that the gas component detection apparatuses be operable with high accuracy notwithstanding such prominent variables.
Heretofore, a gas component detection apparatus has been known which employs transition metal oxides. Such a detection apparatus is mounted for example in an exhaust pipe of an internal combustion engine with the transition metal oxides exposed to the exhaust gases, and the electric resistance variation thereof is detected to determine the air-fuel ratio. However, the electric resistances exhibited by the transition metal oxides vary depending upon not only the concentrations of the gaseous components of the exhaust gases, but also the temperatures thereof. Therefore, in order to determine with high accuracy the air-fuel ratio and thus to effect proper control of the air-fuel ratio, it is necessary to make a temperature compensation, i.e., to compensate for the electric resistance variation of the transition metal oxides due to the temperature of the exhaust gases.